1. Field
The present invention is in the general field of fiber optics, more specifically in the field of lightpipes for transmitting and redirecting light through a solid medium that is light-transmissive.
2. State of the Art
Since the 1970's, right-angle, circuit-board-mounted, lighted indicators have been used to provide visual status information relating to the functions of electronic equipment with which they are used. These have typically been "through-hole" light-emitting diodes (LEDs) with leads bent at a right angle so the direction of light is parallel to the usually horizontally positioned, printed circuit boards on which they are mounted. They are typically directed through a usually vertically positioned front panel of the equipment concerned. Many manufacturers have designed right-angle, plastic housings for mounting flush on the circuit boards to which the LEDs are secured, resulting in easier and more precise X, Y, and Z directional alignment and better stability. A housing provides an alignment advantage over an LED with bent leads when soldering the LED to the circuit board, as well as when installing the circuit board assembly in the equipment chassis.
Some of these housings are designed with means to lock multiple housings together to form an either horizontally side-by-side or vertically aligned array of LEDs. Unfortunately, the design of many of these housings requires that the LED be inserted into the housing by hand and that the LED housing assembly be inserted into the circuit board by hand. Also, those housings that are designed to be locked together typically require human labor to assemble the array. For these reasons, as well as the fact that the housing itself is costly, LEDs in housings have been significantly more expensive than an LED by itself.
Also in the 1970's, lightpipe and fiber optic technology started to gain popularity as a means to redirect and transmit light, either for simple visual indication or for data communication. Later, in the late 1980's and the early 1990's with the increasing popularity of surface mounted LEDs, manufacturers developed ways to combine the automatic insertion advantages of surface mounted LEDs with the alignment advantages of LED housings, this by designing lightpipes and lightpipe arrays which mount to the circuit board and redirect light in the desired direction. These so-called "lightpipes" are again an increased cost over LEDs by themselves, but they require less hand labor to assemble and install and are not required to be installed on the circuit board before the soldering process. An aesthetic benefit of such lightpipes is that it is easy to create various shapes of lightpipe transmission surfaces, for example, as by making a square or triangle shaped indicator using a round LED as the light source.
U.S. Pat. Nos. 5,130,761, 5,327,328, and 5,349,504 disclose lightpipes or lightpipe arrays fabricated from a transparent material, each providing means for mounting the lightpipe or lightpipe array to the circuit board so that the X Y Z alignment issue is adequately addressed. The two latter of these patents also go into detail as to how lightpipes solve problems of weight, stability, and clearance for automatic equipment encountered when using LED housings. It should be noted that U.S. Pat. No. 5,327,328 refers to a method of connecting multiple lightpipes in such a way that an array can be molded as a single piece, while still substantially reducing light mixing from adjacent light sources. Although this method is somewhat successful, we have discovered that, under low light conditions, such method allows "crosstalk" between adjacent lightpipes which may be unacceptable in more critical applications.
The advantages of lightpipes over simple LEDs and LEDs with housings are widely recognized and account for their increasing popularity. Until recently, current use of lightpipes and lightpipe arrays all involved mounting them on the same circuit boards or panels on which the LED is directly mounted. With these known mounting systems, as well as with LEDs and LED housings, the process of assembling the circuit board in the chassis typically requires careful and sometimes difficult alignment of lightpipes with their corresponding holes in the chassis to ensure that the lightpipes are not scratched, dislodged, broken, or otherwise damaged. Mechanical tolerances between lightpipe, circuit board, circuit board-to-chassis mounting, and chassis can make this a time consuming and difficult procedure. Also, once installed in the chassis, the lightpipes are subject to damage due to the shifting of the circuit board and other mechanical components of the assembly through either normal or abusive handling of the equipment.
To overcome these problems, we determined that the lightpipe or lightpipe array must not be directly secured to the same board or panel on which the light source is secured. A creative solution was to mount the lightpipes on the front panel where they "float" above the light sources. Our lightpipe invention was completed before recently granted U.S. Pat. No. 5,481,440 was issued, which patent discloses a lightpipe array whereby the lightpipe has no direct contact with the LED or the surface on which the LED is mounted. As with our invention, the lightpipe is mounted on the front panel, addressing the aforementioned assembly and handling difficulties. However, the disclosure in U.S. Pat. No. 5,481,440, is (as well as current lightpipes in use are) limited to redirecting the light parallel to the mounting surface of the light source, at or above, but never below, the light-emitting end of the light source relative to the mounting surface. Redirecting light so it is emitted between the light-emitting end of the light source and the mounting surface for the light source has solved the problems remaining from the invention disclosed by the aforementioned U.S. Pat. No. 5,481,440. Our improvement provides the advantage of tighter vertical spacing of components within the assembly. This tighter vertical spacing may be necessary in a cramped assembly or may simply provide more freedom to choose the locations of lightpipes on the panel. With our equipment, the tighter vertical spacing was absolutely necessary.
Another problem with current designs is that, for lightpipe arrays, close spacing of adjacent lightpipes exhibit what may be an unacceptable amount of crosstalk between adjacent light sources and lightpipes which likely accounts for the wide spacing of adjacent lightpipes in U.S. Pat. No. 5,481,440.